Vertical Speed / Altitude Tape Indications on Modern PFDs - Howdoesitwork?
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Vertical Speed / Altitude Tape Indications on Modern PFDs - Howdoesitwork?
Dear friends,
On some old COLLINS / HONEYWELL CRTs & most all new LCD Primary FLight Displays, the Vertical Speed display is represented as either a radial arc in the lower right hand corner OR a radial arc juxtaposed to the altitude tape ( IE located in close proximity & next to the altitude tape where the VS arc pointer points in the direction of the altitude tape ). Concerning the latter - I was told that the VS arc pointer will actually point to a target altitude - IE simultaneously give you ( IE point to ) VS & where your target altitude will be ( IE if you carry the VS pointer another 1/4 inch into the altitude tape window - it is pointing to an actual predicted altitude target )
Is this correct ? - Ive never seen this as a training point other than at Boeing. Anyone know for sure how this actually works ?
Any thoughts would be appreciated - Thanks !
This got appended by mistake to a previous message - sorry
On some old COLLINS / HONEYWELL CRTs & most all new LCD Primary FLight Displays, the Vertical Speed display is represented as either a radial arc in the lower right hand corner OR a radial arc juxtaposed to the altitude tape ( IE located in close proximity & next to the altitude tape where the VS arc pointer points in the direction of the altitude tape ). Concerning the latter - I was told that the VS arc pointer will actually point to a target altitude - IE simultaneously give you ( IE point to ) VS & where your target altitude will be ( IE if you carry the VS pointer another 1/4 inch into the altitude tape window - it is pointing to an actual predicted altitude target )
Is this correct ? - Ive never seen this as a training point other than at Boeing. Anyone know for sure how this actually works ?
Any thoughts would be appreciated - Thanks !
This got appended by mistake to a previous message - sorry
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"IE if you carry the VS pointer another 1/4 inch into the altitude tape window - it is pointing to an actual predicted altitude target ) "
It does sound possible that this could be the case, but you would have to know the time frame. Here's a close-up of the V/S pointer at minus 600 (or thereabouts) fpm.
http://members.ozemail.com.au/~b744er/VSpointer.jpg
It seems to be pointing to an altitude of about -100 feet below the current altitude if you are selecting the right hand side of the altitude tape, or -200' if you are selecting the left hand side of the altitude tape). In this case, the time frame could either be 10 or 20seconds. i.e the aircraft would reach minus 100' in 10 seconds if you chose the right hand side of the altitude tape.
However, would this information be of any use to the pilot? The altitude tape only shows a limited range of altitudes.
Regards.
Q.
It does sound possible that this could be the case, but you would have to know the time frame. Here's a close-up of the V/S pointer at minus 600 (or thereabouts) fpm.
http://members.ozemail.com.au/~b744er/VSpointer.jpg
It seems to be pointing to an altitude of about -100 feet below the current altitude if you are selecting the right hand side of the altitude tape, or -200' if you are selecting the left hand side of the altitude tape). In this case, the time frame could either be 10 or 20seconds. i.e the aircraft would reach minus 100' in 10 seconds if you chose the right hand side of the altitude tape.
However, would this information be of any use to the pilot? The altitude tape only shows a limited range of altitudes.
Regards.
Q.
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"Boeing 737NG or 777, 20' below Sea Level, 600fpm descent, right bank of approx 20-40 degrees??? Simulator on your home PC, right?"
Actually, it's a real 747-400, so I'm either making a sharp turn on the approach to an airport below sea-level.... or using the 747-400's Central Maintenance Computer to generate these test signals
Cheers.
Q.
Actually, it's a real 747-400, so I'm either making a sharp turn on the approach to an airport below sea-level.... or using the 747-400's Central Maintenance Computer to generate these test signals
Cheers.
Q.
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The Altitude scale and the VSI scale are totally unconnected- just next to each other. Obviously the altitude scale is evenly ruled, or linear. The VSI is logarithmically scaled- the first thousand feet per minute up or down covers the the same distance on the VSI scale as from 1000 to 4000 fpm up or down. You cannot juxtapose a scale like this against a linear scale like the altimeter tape- they are totally divorced from each other. Anyone who thinks they see a direct relationship must have been smoking something (apart from VSI reads up and altimeter reading increases!). I've been flying glass cockpit for 8 years! (737 and 747)
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"Anyone who thinks they see a direct relationship must have been smoking something"
What part of this forum's rules don't you understand, sir?
Yes, you are right about the indicator, but would I be the first person to be a victim of an optical illusion, even when not under the influence of anything?
Without a knowledge of geometry, would some say that the angled black lines (in the following pic) divide the red line into non-even intervals?
http://members.ozemail.com.au/~b744er/Scale.gif
"I've been flying glass cockpit for 8 years! (737 and 747)"
Good for you, but what this has to do with anything, I don't know. I've been working in glass cockpits for twice that long, but have been known to be wrong now and then.
Q.
What part of this forum's rules don't you understand, sir?
Yes, you are right about the indicator, but would I be the first person to be a victim of an optical illusion, even when not under the influence of anything?
Without a knowledge of geometry, would some say that the angled black lines (in the following pic) divide the red line into non-even intervals?
http://members.ozemail.com.au/~b744er/Scale.gif
"I've been flying glass cockpit for 8 years! (737 and 747)"
Good for you, but what this has to do with anything, I don't know. I've been working in glass cockpits for twice that long, but have been known to be wrong now and then.
Q.
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I was just positively trying to make the point that there is absolutely no correlation between the Altitude tape readings and the VSI indicator readings. I did not mean to cause you any offence, but to try and follow up a lead that there is a mysterious linkage between to two is barking up the wrong tree. If we examine your second diagram and graduate the red line into 500fpm divisions for each marker, it's easy to see when you try and correlate with the altitude scale that there is no way to do it. My apologies if my manner was abrupt- I'm like that- ask my ex-wife!
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I spoke to a FLight Deck Engineer who invented the display layout - & he told me that this is the way the thing is supposed to work ! IE That you can predictively reach a particular altitude based on the indicated VS - IE The reason they are juxtiposed - is so that the VS indicator simultaneously points to the altitude tape & to a particular altitude at that - I was mildly flabbergasted - because I too have been familiar with glass for years - but was unaware of this relationship between the two displays - particularly when Honeywell put a dial VS display in the corner on many A/Ps ..I have never seen the dual interrelated display concept trained to as a training point though ..
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Well looking at my manual with a ruler, 1000fpm is pointing at an altitude just over 200 feet different, and 2000fpm is pointing at an altitude 500 feet different. Beyond that, the VSI is unreadable. IF I was designing such an instrument, I would have had it similarly next to the altitude tape as an indicator that when this one is pointing up, that one will go up too. One looks at both together as they are completely interrelated, so the null point of the VSI should point to current altitude. If we are saying it's predictive for 15 seconds time, then this will quickly break down beyond a few thousand fpm that it is strictly an academic design exercise and of no practical value whatsoever.
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"I spoke to a FLight Deck Engineer who invented the display layout - & he told me that this is the way the thing is supposed to work ! "
U2FB....
The only way it could work was if the V/S scale was linear... at least on the type shown in the pic.
I now recall that a variation of this trick could be used to scale down/up drawings (a tip from my Technical Drawing classes in High School).
Notso....
You are a gentleman and a scholar. All is forgiven.
Regards.
Q.
U2FB....
The only way it could work was if the V/S scale was linear... at least on the type shown in the pic.
I now recall that a variation of this trick could be used to scale down/up drawings (a tip from my Technical Drawing classes in High School).
Notso....
You are a gentleman and a scholar. All is forgiven.
Regards.
Q.
I don't fly glass but I think there is an alternative possibility: Use the VSI pointer to lead the level off. By this I mean at a given ROC/ROD, wait for the target altitude to move into line with the VSI pointer then pitch to maintain the alignment. This would cause a constantly reducing VS in proportion to proximity to the target altitude. Keep the VSI pointing at the altitude & you'll end up level at that altitude.
I often use a similar technique using mechanical HSIs to intercept a VOR/LOC radial. I keep the lubber line 'touching' the top of CDI and it gives a quite smooth intercept. There is a caveat: If there is a headwind component during the intercept then at some point the intercept will cease. Not a totally bad thing since when it happens the current heading corresponds very closely with the drift allowance that will be needed.
I often use a similar technique using mechanical HSIs to intercept a VOR/LOC radial. I keep the lubber line 'touching' the top of CDI and it gives a quite smooth intercept. There is a caveat: If there is a headwind component during the intercept then at some point the intercept will cease. Not a totally bad thing since when it happens the current heading corresponds very closely with the drift allowance that will be needed.
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I do believe Tinstaafl is a genius - this I believe is how the VSI & Altitude tape - side-by-side orientation is supposed to work - again, I was told this by the flight deck inventor of this particular EADI configuration - he said this is how his flight deck group defined this to Honeywell & Collins & whoever else builds these damn things, but does not think many pilots are aware of this Modus O..
I agree an esoteric exercise ..
I agree an esoteric exercise ..
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I was enlightened by a former test pilot - apparently, the VSI on SOME of the displays ( we're talking about the altitude tape & VSI indicators being juxtiposed variety ) have thwe VSI scale graduations displayed/placed in a non-linear - logarithmic-like manner - IE the scale distance from 0 to 1 is longer than from 2 to 3 etc. Which allows them to effectively be used together in a predictive fashion.
Thanks for your input
Thanks for your input
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<<Keep the VSI pointing at the altitude & you'll end up level at that altitude.>>
Very interesting. I shall apply this tonight and see how it works. Bit weird though- why keep it such an excellent secret from the customers who will use it?
Very interesting. I shall apply this tonight and see how it works. Bit weird though- why keep it such an excellent secret from the customers who will use it?
Bit weird though- why keep it such an excellent secret from the customers who will use it
I did an evaluation at Swissair back in the day, and one of the requirements was a sim flight (simple thing, no visuals just instruments).
As a pretty much 0 hours ab initio candidate I did a similar thing instinctively and without being told to. Just thought it was a good way of getting a smooth level out without overshooting - I did the same in the turns using the HSI, easing off the bank angle following the pointer as the target heading entered it's last 20'.
Now am I a genius natural pilot ?
Not really. Didn't get in to Swissair.
Thank the lord....
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Its no secret to Boeing training apparently it is a training point on the glass PFDs training footprint.. Thanks all for the enlightening - though a bit Socratic discussion ..
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To give practical feedback as I experienced it, it is impossible to use it effectively. Firstly, VSI experiences lag- well known. To pretend that the VSI needle is pointing to desired altitude and 'fly' it to null (at which point you should be at desired altitude) doesn't work. It means you are transferring significant attention to VSI, which is telling you nothing useful, trying to extrapolate altitude reading when you should be giving all your attention to what counts:
Altitude
Attitude
Rate of closure
Speed
Plus the others like Heading
I realised that the speed of the movement of the altitude tape is all the cue you need of VS, plus where your desired altitude is on it and how displaced your are. The only time the silly little VSI needle is useful is on final approach- you want about 800fpm, sound a warning at 1000+fpm close to the ground.
This is only my personal opinion. I realise many will not agree, but it has to be appreciated that because of the large scale movement of the VS needle, it is only practical to extrapolate on it across to the altitude tape to not more than a maximum of about 700fpm.
Altitude
Attitude
Rate of closure
Speed
Plus the others like Heading
I realised that the speed of the movement of the altitude tape is all the cue you need of VS, plus where your desired altitude is on it and how displaced your are. The only time the silly little VSI needle is useful is on final approach- you want about 800fpm, sound a warning at 1000+fpm close to the ground.
This is only my personal opinion. I realise many will not agree, but it has to be appreciated that because of the large scale movement of the VS needle, it is only practical to extrapolate on it across to the altitude tape to not more than a maximum of about 700fpm.
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Firstly, VSI experiences lag- well known
p.s. QAVION, you got any more pics like that, trying to put a mini manual together (self use) and might be able to use some of them?
Last edited by jtr; 5th Aug 2003 at 19:25.
